FEATURE ARTICLES NATURAL -C OLOR PINK , P URPLE , RED , AND BROWN DIAMONDS : BAND OF MANY COLORS Sally Eaton-Magaña, Troy Ardon, Karen V. Smit, Christopher M. Breeding, and James E. Shigley Among fancy-color diamonds, naturally pink to red stones are among the rarest and most valuable. The color origin for natural pink diamonds is due to either absorption from the as-yet-unidentified “550 nm” defect(s) that are correlated with shear stress and natural plastic deformation or, very rarely, the NV 0/– centers (nitrogen combined with a vacancy). In this article we summarize prior research as well as the physical characteristics of more than 90,000 natural pink, orangy pink, red, purple, and brown diamonds from the internal GIA database. (Browns and purples are included here, as they coexist on a color continuum with pink diamonds.) We also present absorption and luminescence spectra on a representative subset of 1,000 diamonds to provide an un - paralleled gemological and spectroscopic description of these rare gemstones. For pink diamonds, the gemo - logical observations closely correlate with diamond type and the extent of nitrogen aggregation (i.e., type IaA<B, type IaA>B, and type IIa pinks show distinct characteristics). Since type IaA<B diamonds are predominantly sourced from the Argyle mine, which is scheduled to close in the next few years, we distinguish the properties of these pink diamonds from the others studied. iamond is one of Earth’s most extraordinary ish pink to pinkish brown, pink, red, purple, and un - materials. It represents the pinnacle for sev - modified brown diamonds. Although this article cov - Deral material and physical properties. As a gem, however, it is the near-perfect examples—dia - monds attaining the D-Flawless distinction—and those with imperfections resulting in a vibrant or surprising color that create the most enduring im - In Brief pressions. Fancy-color natural diamonds are among • Almost all pink/purple/red/orangy pink diamonds owe the most highly valued gemstones due to their at - their color to the presence of an as-yet-unidentified tractiveness and great rarity. The 18.96 ct Winston 550 nm absorption band. Minor differences in band Pink Legacy, with a color grade of Fancy Vivid pink, characteristics along with the presence of other defects recently made history by selling at over $50 million, (such as N3 and H3) lead to differences in hue and its $2.6 million per carat price an all-time high for a saturation. pink diamond (Christie’s, 2018). • Among “pink” diamonds colored by the 550 nm band, This article is the third in a series of studies on distinctions in color distribution and observed strain can be correlated with their diamond type. natural colored diamonds: Breeding et al. (2018) dis - cussed the color origin of green diamonds, and Eaton- • A sizable percentage of the “pink” diamonds studied, Magaña et al. (2018) dealt with blue/gray/violet particularly those with saturated colors, are consistent with material found at the Argyle mine, scheduled to diamonds. Here we summarize the color origin of close in 2020. orangy pink, purplish pink to pinkish purple, brown - See end of article for About the Authors and Acknowledgments. ers a wide variety of color descriptions compared to, GEMS & G EMOLOGY , Vol. 54, No. 4, pp. 352 –377, http://dx.doi.org/10.5741/GEMS.54.2.352 for example, the first article in the series, which was © 2018 Gemological Institute of America limited to natural diamonds with only green as the 352 NATURAL -C OLOR PINK DIAMONDS GEMS & G EMOLOGY WINTER 2018 Figure 1. The 34.65 ct Princie (center, photo courtesy of Christie’s) is a famous example of a pink diamond colored by NV 0/– centers. It is flanked by an array of natural brown, brown-pink, orangy pink, purple-pink, and pink dia - monds with the far more common cause of color—the 550 nm absorption band. These examples span the diverse color range of pinks submitted to GIA. The photos in this compilation are not imaged to scale. dominant description, the color descriptions are ral “pink” diamonds, principally colored by an as-yet- joined here, as the vast majority of them (which will unidentified “550 nm” absorption band, in order to be quantified below) contain the 550 nm band as a help the trade better understand how these beautiful prevalent absorption feature. For the sake of simplic - diamonds with extremely valuable colors originate. ity, this broad range of color descriptions (e.g., figures 1 and 2) will generally be shortened to “pink” in this CAUSES OF COLOR article. All colored diamonds submitted to GIA are subject Previously, several aspects of gem-quality “pink” to a variety of spectroscopic analyses. The analytical diamonds have been addressed, such as their gemo - techniques and specific details of the instrumenta - logical characteristics (e.g., King et al., 2002); their tion and methods used are summarized in Breeding defects and associated spectroscopic features (e.g., et al. (2018; see supplementary table S-1 at Titkov et al., 2008; Deljanin et al., 2008; Fisher et al., https://www.gia.edu/gems-gemology/spring-2018- 2009; Gaillou et al., 2010; Stepanov et al., 2011; natural-color-green-diamonds-beautiful-conundrum). Byrne et al., 2012a,b; Titkov et al., 2012; Gaillou et “Pink” color in diamonds spans a wide range in al., 2012; Howell et al., 2015); and reports on notable the GIA color description terminology (figure 2; King “pink” diamonds (Smith and Bosshart, 2002; King et et al., 1994; King, 2006). In this article, we include all al., 2014). Here we review the published literature natural fancy-color diamonds with pink, purple, or and supplement it by compiling results obtained red as the dominant hue (i.e., the final name in the from 90,000+ natural diamonds recorded in the GIA color description) in addition to unmodified brown. internal database. Diamonds with yellow-brown or orange-brown color Our purpose is to provide a detailed account of the will be discussed in an upcoming article. In the full gemological and spectroscopic characteristics of natu - dataset of 90,000+ “pink” diamonds seen at GIA be - NATURAL -C OLOR PINK DIAMONDS GEMS & G EMOLOGY WINTER 2018 353 Increasing Saturation Very Light pink Light pink Fancy Light pink Fancy pink Fancy Intense pink Fancy Deep pink Fancy red Increasing Brown Increasing Orange Fancy brown Fancy pink-brown Fancy brown-pink Fancy brownish Fancy Intense orangy Fancy Vivid pinkish orangy pink pink orange Increasing Purple Fancy Vivid purplish pink Fancy Intense purple- Fancy pink purple Fancy Vivid pink purple Fancy Vivid purple pink Figure 2. These examples of diamonds with varying hues and color saturations represent the “pink” color ranges. Photos by GIA staff. The photos in this compilation are not imaged to scale. tween January 2008 and December 2016, the highest Various colors and representative visible-near infrared percentage were unmodified pink (40%), followed by spectra are shown in figures 2 and 4, respectively. pinkish purple to purplish pink (28%), brownish pink to pinkish brown (17%), and orangy pink (10%); see Colored Deformation Lamellae. In many brown, the color distribution in figure 3. The rarest colors pink, and purple diamonds, the color is concentrated were unmodified brown (3%); purple with brown or within parallel narrow bands (referred to as “brown gray modifiers (1%); unmodified red (0.5%); red with graining,” “pink graining,” or glide planes, or alterna - brown, purple, or orange modifiers (0.4%); and, least tively as a more generalized term of colored lamellae). of all, unmodified purple (0.05%). When manufactured as cut stones, these are typically In the description of color grades, it is more difficult oriented to minimize the face-up appearance of the for the eye to interpret subtle hue differences for very lamellae, resulting in an apparent even color distribu - light-colored diamonds than it is for more saturated di - tion through the table facet. Since the lamellae are amonds (King et al., 1994; King, 2006). For the lightest along the {111} plane, these pink diamonds are gener - color grades, therefore, fewer hue names are used and ally oriented such that the table facet is {100} (J. Chap - the color description spans a wider portion of the hue man, pers. comm., 2018). Micro scopic observation of wheel. Among unmodified pink diamonds, 54% were the lamellae is best accomplished looking through Faint, Very Light, or Light in color (figure 3, right). the pavilion facets of the diamond. Below we chronicle the main causes of color in the These colored lamellae are caused by shear stress form of various structural defects, through which and natural plastic deformation (figure 5, A and B). “pink” diamonds can be divided into different groups. Deformation to form these lamellae only occurs dur - 354 NATURAL -C OLOR PINK DIAMONDS GEMS & G EMOLOGY WINTER 2018 COL OR D ISTR IBU TION 35% N Unmodified pink diamonds O I T 30% All others (inc luding purple- Bro wnish pink A pink, orang y pink, bro wn- R to pinkish S U pink, etc.) T bro wn, 17% D 25% Bro wnish orang y A N S Pinkish purple to pink to orang y / O purplish pink, 28% pink,10% E M N 20% A O I T Bro wn, 3% D F " 15% K O Purple/bro wn- N N purple/gray- I P O purple, 1% " I 10% T N I Pink, 40% U Red/bro wn-red/orange-red, B I 5% 0.9% R T S I D 0% Faint Very Light Fancy Fancy Fancy Fancy Fancy Fancy Light Light Intense Vivid Deep Dark Figure 3.